Field of the Invention. This invention relates to rate monitors, and more particularly to an auto-ranging digital rate monitor in which a number of event pulses accumulated, the number preselected as a function of the rate of the event pulses, and the time elapsed in accumulating the pulses are used in calculating the rate of occurrence of the event pulses.
Description of the Prior Art. There are basically two types of rate monitors, one of which operates on the gate-time principle and the other of which operates on the principle of measuring the time interval between consecutive event pulses. In the first approach, event pulses are gated to a pulse counter during a time interval of a preselected duration. The number of pulses counted and the fixed time are used in calculating the rate of the pulses. However, since the time is fixed, this type of rate monitor does not provide rapid response at low input rates without producing a large inaccuracy.
In the other type of rate monitor, a first event pulse of a series is used to enable a gate which passes timing pulses at known frequency to a pulse counter. The next event disables the gate so that the number of timing pulses counted corresponds to the elapsed time between the two event pulses. Most rate monitors of this type suffer the disadvantage of being able to measure every other period to allow time for the rate calculation. An improved rate monitor of this type, disclosed in U.S. Pat. No. 4,093,850 allows for measurement of the time interval between every pair of consecutive event pulses by performing measurement of a given period and rate calculation for the previous period concurrently.
In both types of units, an added degree of resolution can be obtained through the use of range select switches which are manually operable to increase, or decrease, the time interval during which event pulses are counted, or to increase, or decrease, the rate of the elapsed time pulse generator. However, the need for manual range selection requires that the user select the range which affords the most accurate reading, and that the user, in the same instances change the selecter range, particularly in applications where the event pulse rate varies over a wide range.